1. Field of the Invention
The present invention relates to printed circuit boards, and particularly to suppression of simultaneous switching noise (SSN) in a printed circuit board (PCB).
2. Description of Related Art
As the density of integrated circuits on PCBs increases, the problems associated with signal switching noise become greater. Many integrated circuits have a large number of input/output (I/O) drivers. Several hundred drivers may be present in integrated circuits, and this number will undoubtedly become greater as packaging density increases in the future. Noise that occurs in the PCB when a large number of drivers simultaneously switch from one state to another is known as SSN. The problem may be even more acute when the drivers all switch in the same direction (e.g. high to low). When a large number of drivers switch simultaneously, various signal integrity problems may occur. For example, a conventional PCB as shown in FIG. 4 includes a ground plane 100, a power plane 200 insulated from the ground plane 100 by a fiberglass material, and two integrated circuits A, B positioned on a surface plane (not shown) of the PCB. The power plane 200 includes two power modules 210, 220 insulated from each other by an insulating medium 230 made up of fiberglass material to respectively provide power supply for the integrated circuits A, B. When drivers in the integrated circuit A simultaneously switch from one state to another, SSN from the integrated circuit A can be transmitted to the power module 220 via the power module 210 and an equivalent coupling capacitance formed by the power modules 210, 220 and the insulating medium 230. Then the integrated circuit B may receive the SSN and cause incorrect actions.
What is needed, therefore, is a PCB with suppressed SSN therein.